Microwave attenuator and method of making same



Aug. 26, 1969 J. o. BRAMICK ETAL 3,464,037

MICROWAVE ATTENUATOR AND METHOD OF MAKING SAME Filed Aug. a. 1966INVENTORS JOHN O, BRAMICK CHARLES W. DFEYEF?` BY V/ f ATTORNEY.

United States Patent O 3,464,037 MlCROWAVE ATTENUATOR AND METHOD FMAKING SAME John 0. Bramick, Bernardsville, and Charles W. Dreyer,

Morris Plains, NJ., assignors to Miemlab, Livingston,

NJ., a corporation of New Jersey Filed Aug. 8, 1966, Ser. No. 570,850Int. Cl. H01p 1/22 US. Cl. 333-81 11 Claims ABSTRACT OF THE DISCLOSURE Acoaxial attenuator comprising a unitary central resistance elementhaving a contact intermediate its ends which is electrically connectedto the central resistance element. A radially extending disc is mountedon the central element and is provided with a second contact inoverlying relationship to the first contact. The first and secondcontacts are soldered together to mechanically and electrically connecttogether the central resistance element and the disc. Contact means isprovided on the central resistance element and the disc resistanceelement for connecting the attenuator in an electrical circuit with atransmission line.

A method for fabricating the attenuator also is disclosed.

This invention relates generally to a construction for a microwaveattenuator and to a method of making the same and, more particularly,pertains to a microwave attenuator which has a relatively constantattenuation characteristic over an extremely wide frequency band.

Piand Tee-network attenuators are used in high frequency coaxial cablesor microwave transmission lines to reduce the power flowing in the cableby a known ratio. A Tee-network attenuator, for example, includes twoseries resistors which are connected together by a screw arrangement toprovide a central resistor assembly. A disc resistor receives the screwtherethrough and is sandwiched between the two series resistors. Thecentral resistor assembly is serially connected in the center conductorof the coaxial cable while the disc resistor is connected to the outerconductor of the coaxial cable by a pluralitycf spring clips. The discis maintained in place between the two series resistors and inelectrical contact therewith by the pressure of the series resistorswhich abut opposite surfaces of the disc. While this type of Tee-networkattenuator construction is easy to assemble, it has a number of severedisadvantages associated with its use. i

More specifically, the mechanical screw connection between the twoseries resistors requires that the resistors be separated by anextremely large length as compared to the wavelength of the microwavefrequencies under consideration. This separation represents an impedancediscontinuity which requires appropriate compensation techniques. Suchcompensation becomes exceedingly difficult to obtain at highfrequencies. Additionally, the fact that the disc is electricallyconnected to the series resistors by means of a contact pressure alsocontributes to the non-uniform operation of the above-described network.That is, the elements comprising the network expand and contract atdifferent rates when the ambient temperature changes. The resultantpressure changes cause variations in the value of the network. Alsocontributing to the instability of networks of this type is theparticular method which is commonly used to provide contacts on theresistors. Thus, the contacts are provided by electroplating smallcontact bands over resistive films which provide the resistive elementsof the 3,464,037 Patented Aug. 26, 1969 network attenuators. These bandscreate discontinuities in the form of stray series and shuntcapacitances. These capacitances have an adverse effect on theattenuation characteristics of the network.

The above-mentioned limitations severely limit the frequency range ofattenuators of the type described. For example, Tee-network attenuatorshave been found to operate only as high as 5-8K rnc. while Pi-networkshaving a similar construction have an upper frequency limit of only 3-4Kmc.

Accordingly, the desideratum of the present invention is to provide anattenuator construction capable of efciently operating up to at least18K mc. without degradation of the electrical characteristics of theattentiator.

Another object of the present invention is to provide an attenuatorconstruction wherein respective resistors comprising the attenuator aresoldered to each other to eliminate variations in the value of theattenuator due to changes in contact pressure between the resistiveelements.

A further object of the present invention is to provide an attenuatorconstruction having reduced contact band surfaces to substantiallyYeliminate abrupt changes in impedance between the elements comprisingthe attenuator.

Another object of the present invention is to provide an attenuatorconstruction wherein the resistors comprising the attenuator areassembled in one homogeneous unit which includes its own housing tofacilitate connection of the attenuator in a coaxial cable.

Still another object of the present invention is to provide a method forcompletely and easily assembling an attenuator for the attenuation ofmicrowave frequency signals.

The attenuator of the present invention includes a rod having aresistive film thereon. yIf it is desired to provide a Tee-networkattenuator, a contact is provided on the rod and it is approximatelycentrally located thereon. A disc resistance is placed on the contactand a preformed ring of solder is received between the contact and thedisc. Two bushings are placed about the rod and disc combination so thattheir ends engage an outer contact on the disc resistance. A preformedsolder ring is received between the ends of the bushings. Heat isapplied to the assembly tomelt the solder rings thereby to firmlyconnect the disc resistance with the rod resistance and the vbushingswith the disc resistance.

A feature of the present invention is to provide an attenuatorconstruction which may utilize solder having a preformed shape toconnect the elements comprising the attenuator together.

Other objects and advantages of the present invention will become moreapparent from a consideration of the following detailed description whentaken in conjunction with the accompanying drawings, in which:

FIG. l is a sectional view of a Tee-network attenuator constructed inaccordance with the present invention;

FIG. 2 is a vertical sectional View ofthe rod resistor portion of theattenuator shown in FIG. 1;

FIG. 3 is a vertical sectional view of the disc resistor shown in FIG.1; and

FIG. 4 is an exploded View of an attenuator assembly constructedaccording to the present invention.

The attenuator construction of the present invention will be describedin conjunction with the fabrication of a Tee-network attenuator.However, the present invention is not to be interpreted as being limitedto this type of attenuation network since the invention described hereinbelow is equally applicable to Pi-network attenuators. That is, peopleskilled in the art will readily recognize that the Tee-networkattenuators described hereinbelow may easily be converted to aPi-network attenuator.

A Tee-network attenuator assembly is designated generally by the numeralin FIG. 1 and comprises a rod 12, a disc 14 centrally mounted on the rod12, and respective bushings 16 and 18 which are connected to the disc14. The rod 12 provides the two series arms of the Teenetwork attenuatorwhile the disc 14 provides the shunt arm therefor. Contacts 20 and 22are provided on the ends of the rod 12 and are adapted to be connectedto the central conductor of the coaxial cable (not shown). The outerconductor of the coaxial cable is adapted to be connected to thebushings `16 and 18.

The rod 12 is shown in detail in FIG. 2 and includes a centralinsulating core 24 having reduced diameter end portions 26 and 28. Thecore 24 may be comprised of any insulating material such as a ceramic orglass. Deposited on the core 24 is a carbon film 30. The carbon film 30provides the central series arm resistors of the assembly 10 in themanner noted below. Plated on the carbon film 30 about the reduceddiameter end portions 26 and 28 are respective nickel contacts 32 and34. A nickel band 36 is plated on the carbon film 30 intermediate theends of the rod 12. Then band 36 is centrally located on the rod. Platedto the respective nickel contacts 32 and 34 and the band 36 arerespective silver contacts 20, 22 and 42.

The central contact bands 36 and 42 essentially divides the resistivefilm 30 into two serially connected resistive arms. Hence, by utilizinga construction of this type the former construction which required theuse of a screw assembly to connect the series arms of the attenuationnetwork is eliminated. Accordingly, the two series arms of theattenuation assembly 10 are separated by a distance which issubstantially smaller than the distance between the series arms of theprior art construction. That is,`in the present invention, the twoseries arms are separated only by the Width of the central contacts 36,42. Accordingly, this reduction in the spacing between the resistiveelements allows the Tee-network attenuator of the present invention tobe used at much higher frequencies than the attenuators used heretofore.

The disc resistor 14 as shown in detail in FIG. 3 and comprises anannular core 44 having a central aperture 46. Similarly to the core 24,the core 44 may be comprised of any insulating material such as aceramic or glass. Deposited about the exterior surfaces of the core 44is a carbon film 48 which forms the resistance portion of the core 44.Plated about the peripheral wall of the carbon film 48 is a circularnickel contact 50. Plated on the nickel contact 50 is a circular silvercontact 52. Similarly, plated on the wall of the carbon film 48surounding the wall defining the aperture 46 is a nickel contact 54. Thesilver contact 56 is plated on the nickel contact 54.

The assembly of the Tee-network attenuator 10 may best be understoodwith reference to FIG. 4. Thus, in fabricating the assembly 10 apre-formed ring of solder 58 is received about the center contact 42 ofthe rod 12. The disc 14 is then slid over the contact 42 so that thesolder ring 58 is in tight frictional engagement with the contact 42 onthe rod 12 and the contact 56 on the ring 14.

The bushings V16 and 18 are provided with respective central throughbores 60 and 62. Respective recesses 64 and 66 are provided adjacent theinner ends of the bushings 16 and 18 to define respective peripheralanges 68 and on the respective bushings. The recesses 64 and 66 aresized to receive the disc 14 therein with the peripheral flanges 68 and70 in engagement with the outer contact 52 of the disc 14. A preformedring of solder 72 is received between the ends of the peripheral flanges68 and 70 of the respective bushings 16 and 18.

Heat is then applied to the assembly 10 suilcient to cause thesolderrings 58 and 72 to melt. Accordingly, the

solder ring 58 will connect the rod 12 with the disc 14' to provide agood electrical connection therebetween. Similarly, the ring 72 willmelt to connect the outer conductor 52 of the disc 14 with the bushings16 and 18 to provide a good electrical connection therebetween. It is tobe noted that the bores 60 and 62 are sufficiently large so that the rodY12 will be in spaced relation with respect thereto.

The central band 42 on the rod 12 is made substantially equal to thewidth of the disc 14. Hence, the two series resistors which are formedon the rod 12 terminate just at the point where the disc resistorbegins. Accordingly, there are no abrupt changes in resistance betweenthe rod and the disc and, additionally, the three lresistors arecombined into one homogeneous assembly 10.

As noted hereinabove, a Pi-network attenuator may be provided utilizinga construction and method similar to that described above in connectionwith the Tee-network attenuator assembly 10. That is, instead ofproviding one essential band on the rod 12, two bands may be providedadjacent each end which receive discs thereon to provide the shuntresistance arms of the Pi-network.

Accordingly, an attenuation network has been described whichsubstantially eliminates the effect of dimensional irregularities causedby wide spacings between the resistive elements comprising theattenuator network.

Additionally, the construction of the present invention substantiallyeliminates pressure contact resistance to improve the over-allmechanical stability of the attenuation network and to allow a reductionin the size of contact bands thereby to reduce the effects of straycapacitances.

While the preferred embodiment of the present invention has been shownand described herein, it will become obvious that numerous, omissions,changes and additions may be made in such embodiment without departingfrom the spirit and scope of the present invention. That is,multi-section Pior Tee-network attenuators may conveniently be realizedby the present construction to obtain high attenuation values in thoseapplications in which individual yresistor values become difficult torealize in practice. For example, the cascading of two Tee-networkattenuators may be accomplished by providing a single elongatedresistance rod having two contact bands adjacent to and spaced from eachend of the rod to define three sections. Each outer section representsthe series arm of separate Tee-networks and the resistance of theintermediate section is equal to the sum of the arms of the twoTee-networks connected in series. Disc resistors are mounted on the twocontact bands to provide the shunt armv resistances for Tee-network.Accordingly, many such cascaded stages may be provided as desired simplyby providing a sufficiently long rod having the desired characteristicsthereby to provide an extremely compact assembly.

What is claimed is: 1. A coaxial attenuator comprising a unitary centralresistance element,

at least a first contact intermediate the ends of and electricallyconnected to said central resistance element,

an outwardly extending resistance element,

a second contact on said outwardly extending resist* ance element,

said outwardly extending resistance element being mounted on saidcentral resistance element with said second contact in overlyingrelation to said first contact,

connecting means for lixedly and electrically connecting said first andsecond contacts together whereby said central resistance element andsaid outwardly extending resistance element are fixedly connectedtogether,

and contact means on said central resistance element and said outwardlyextending resistance element for connecting said attenuator inelectrical circuit with a transmission line.

2. A coaxial attenuator as in claim 1,

in which said first and second contacts are coextensive with each other.

3. A coaxial attenuator as in claim 1,

wherein said first contact is centrally located on said centralresistance element,

said first contact dividing said central resistance element intorespective series arms which terminate at said first contact.

4. A coaxial attenuator according to claim 3,

in which said central resistance element is in the shape of a rod,

and said first contact comprises a conducting band surrounding said rod.

5. A coaxial attenuator as in claim 1,

wherein said outwardly extending resistance element comprises a dischaving a central aperture,

said second contact being positioned about the wall defining saidaperture in said disc,

said connecting means comprising a solder connection Ibetween said firstand second contacts.

6. A coaxial attenuator in accordance with claim 5,

in which said disc is provided with an outer contact about the peripheryof said disc,

and a pair of opposed bushings,

each of said bushings having a recess to receive opposed surfaces ofsaid disc therein,

and means for Iixedly and electrically connecting said pair of bushingswith said outer contact. 7. A coaxial attenuator according to claim 6,wherein said means for fixedly and electrically connecting said pair ofbushings and said disc comprises a solder connection.

-8. A coaxial attenuator as in claim 7, wherein each of said pair ofbushings is provided with a central through bore,

said central through bores receiving different portions of said centralyresistance element therein in spaced relation to the Walls dening saidcentral through bores.

9. A method for making a coaxial attenuator com* prising providing a-rod resistance element having at least one contact thereon,

and a disc resistance element having an aperture defined by a contactsurface,

mounting said disc on said rod with a pre-formed solder ring receivedbetween the contact on said rod resistance element and the controlsurface on said disc,

and heating said solder ring to cause said solder to melt.

10. The method of claim 9,

including the further step of cooling said solder to cause said solderto solidify whereby said rod and said disc are Iixedly and electricallyconnected to each other.

11. The method of claim 9,

including, before heating said solder ring,

the further steps of providing a pair of bushings to receive the opposedfaces of said disc,

placing the bushings about said disc with a preformed solder ringreceived therebetween,

heating the solder ring received between said rod and disc resistanceelements and said bushings to cause said solder rings to melt,

and cooling said solder after it has melted to solidify said solderwhereby said rod and disc and said disc and bushings are xedly andelectrically connected to each other.

References Cited UNITED STATES PATENTS 3,174,123 3/1965 Frederico333--81 2,994,049 7/ 1961 Weinschel.

2,968,774 1/1961 Rodriguez.

2,884,606 4/ 1959 Stevens.

2,884,595 4/1959 Stevens 324-95 2,820,952 1/ 1958 Hancock et al. 333--81HERMAN K. SAALBACH, Primary Examiner C. BARAFF, Assistant Examiner U.S.Cl. X.R.

